Question 23.8: Using these acid dissociation constants for glycine, calcula...

Using these acid dissociation constants for glycine, calculate the ratios [Z]/[C^+] and [Z]/[A^-] at pH 2.00, 6.00, and 10.00.

STRATEGY

Substitute into the general K_a expression where

C^+ = \begin{matrix}& H\\\ & \mid && &\\H-&C-&COOH;\\&\mid \\&{NH_3}^+\end{matrix}Z = \begin{matrix}& H\\\ & \mid && &\\H-&C-&COO^-;\\&\mid \\&{NH_3}^+\end{matrix} A^- = \begin{matrix}& H\\\ & \mid && &\\H-&C-&COO^-\\&\mid \\&NH_2\end{matrix}

For the first dissociation:

C^+(aq) \rightleftharpoons H^+(aq) + Z(aq)                   K_{a1} = 4.6 \times 10^{-3}

For the second dissociation:

Z(aq) \rightleftharpoons H^+(aq) + A^-(aq)                  K_{a2} = 2.5 \times 10^{-10}